Spark-plug and method of manufacturing the same.



F: MfFURBER.

SPARK PLUG AND METHOD OF MANUFACTURlNG THE SAME.

APPUCATION FILED MAR. 17. 1917- 1,228,767 Patented June 1917.

i N VEN TUE WWW UNITED STATES PATENT OFFICE.

FREDERICK M. FURBER, OF REVERE, MASS.ACHUSETTS.

SPARK-PLUG AND METHOD OF MANUFACTURING THE SAME.

Specification of Letters Patent.

Patented June 5, 1917.

Application filed March 17, 1917. Serial No. 155,463.

. provements in Spark-Plugs and Methods of Manufacturing the Same, ofwhich the following description, in connection with the accompanyingdrawings, is a. specification, like reference characters on the drawingsindicating like parts in the several figures.

This invention relates to spark plugs and to methods of manufacturingspark plugs. The exceedingly keen competition which has arisen in recentyears in the spark plug industry has made the adoption of economicalconstructions and methods of manufac ture of these devices a practicalnecessity to the maintenance of a successful business in this line. Atthe same time the users of spark plugs have become more exacting intheir requirements and are demanding a spark plug of a much sturdier andmore substantial construction than has heretofore been required. Thetrade is also demanding a spark plug that is very reliable and issubstantially gas tight under operating conditions; and these changes inthe demands of the trade have, of course, complicated the problemspresented to the spark plug manufacturers. It will readily beappreciated by those skilled in this art that the chief manufacturingdifiiculty resides in the assembling of the insulator in the body orshell of the plug. This difficulty arises primarily from the fact thatthe insulators are relatively fragile and that they vary greatly indimensions. Most of-these insulators are made of porcelain which, ofcourse, warps and becomes distorted in the baking operations,

thus producing extraordinary variations in I dimensions which requirethe use of gaskets or similar means to accommodate these variations andprevent the application of excessive pressure to relatively small areasof the insulator. Even then these variations render it difiicult toapply the pressure necessary to produce a gas tight joint between theinsulators and the shells without breaking the insulators.

The present invention has for its general object to devise a spark plugthat will sat isfy the requirements of the trade and at the same time todevise a plug construction and a method of manufacturing it which willsolvethe problems presented to the manufacturer. Stated morespecifically, the inventlon aims to devise a sturdy, substantial andreliable spark plug which can be economically manufactured and whichwill be so constructed that much of the skill and exactness required inmanufacturing spark plug constructions heretofore proposed will beeliminated.

The invention is particularly concerned with the mounting of theinsulator in the shell or body of the plug.

The invention will be readily understood from the following description,reference being made to the accompanying drawings, in which:

Figure l is a view in perspective of a spark plug embodying theinvention;

Fig. 2 is a vertical cross sectional view of the plug shown in Fig. 1-;

Fig. 3 is a side elevation of a part of the spark plug, showing a stepin the process of manufacture Fig. 4 is a fragmentary cross sectionalview, on a large scale, of a part of the spark plug shown in Figs. 1 and2;

Fig. 5 is a cross sectional view, partly in elevation, showing the sparkplug and one of the tools that operates on it;

Fig. 6 is a View, partly in vertical cross section and partly in sideelevation, showing the apparatus which distorts the shell to clamp theinsulator therein; and

Fig. 7 is a cross sectional View of a part of a modified form of plug.

The plug shown comprises a shell or body 2, which may be made out ofcold rolled stock of hexagonal cross section, the lower part of thisshell or body being turned down to form a shank which is screw threadedto adapt it to be secured in an engine cylinder. The shell is drilled toform a bore therethrough and is counterbored from its outer end, thatis, the end which projects out of the engine cylinder when the plug isin use, to form an internal shoulder or seat 4. An insulator 6 ispositioned in the bore of the shell 2 and is provided with acircumferential enlargement 7, the ends of which form upper and lowershoulders 8 and 9, respectively. The shoulder 4 in the shell forms aseat for the lower shoulder 9 of the insulator 6, a gasket 10 beinginterposed between this seat and the shoulder.

The insulator is held in the shell by means of an annular flange 12formed integrally with the shell 2 at its outer end and turned inwardlyover the upper shoulder 8 of the insulator into position to clamp the enlargcment 7 of the insulator securely against the seat 4. Preferably agasket 14 is interposed between the shoulder 8 and the flange 12 toprotect the shoulder. It will be noted that the enlargement 7 of theinsulator is so much smaller in diameter than the bore of the shell thata lateral clearance is provided between the shell and the peripheralsurface of the enlargement 7. The insulator thus is secured in the shellsolely by the parts that engage the shoulders 8 and 9.

Accordin to the preferred method of manufacturing the plug, theinsulator and shell are made in the usual way but the shell 2 isprovided with an annular flange 12 at its outer end, as shown in Fi 6.The gaskets 10 and 14 are then place on the shoulders 9 and 8,respectively, and the shell is inserted in the plug in its normal oroperative position. The shell 2 then is supported in an upright positionin a die 16, as shown in Fig. 6, and another die or swaging tool isemployed to turn the flange 12 inwardly or crimp it over the shoulder 8.It will be noted that while the flange 12 is relatively thin ascompared-with the main body of the shell, it is thicker than the flangeusually employed in s ark lugs of this general construction. uch angesheretofore have been made very thin so that they could be crimpedreadily over the upper shoulder of the insulator; and according to theprocesses heretofore followed in the assembling plugs of this type theflange has been crimped or turned over at a single operation. In someinstances the flanges are heated sufficiently to render them relativelyplastic so that they can be distorted more readily. In all of thesecases, however, difiiculty has been encountered in handlin insulators inwhich there is an apprecia 1e variation in the height of the enlargementat different points circumferentially thereof. I It will readily beappreciated that if the flange 12 of the insulator were turned in by abell-shaped die, of the character usually em loyed, or by spinning, andthe enlargement were appreclably higher on one side than the other, thehigh side would be subjected to much greater pressure than the low side;and the probable result would be either to break the insulator or elseto leave the flange in such a condition that the plug would not be gastight on the low side of the insulator.

According to the present invention the flange is turned in, or crimped,in such a manner that it clamps the enlargement of the insulator againstthe seat 4 with a pressure which is substantially uniform at all pointscircumferentially thereof.

Referring now to Figs. 3 and 6, it will be seen that the upper diecomprises two members 18 arran ed to operate on the flange 12 atdiametrica ly opposite points, (using the term points, not in itsgeometrical sense,

but rather in the sense of designating a relatively small area). Themembers 18 are both secured pivotally to a yoke 20 and are held in aproperly spaced relation to each other by guides 22. These upper diemembers 18 are reciprocated toward and from the lower die 16 in adirection parallel to the axis of the spark plug. The mechanism by whichthis movement 1s produced, may comprise a plunger 24 connected to theyoke 20 by-a pivot 26, which is mounted in the yoke and passes through aslot 28 in the lower end of the plunger. A stifi coiled spring 30surrounds the plunger 24 and bears at one end against the yoke 20 and atits opposite end against a head 32 with which the plunger is provided. Apower driven mechanism of some kind may be employed to act through thehead 32 to apply pressure to the upper die, and the arrangement justdescribed equalizes this pressure between the two die members 18 whichact directly on the flange 12. v

As clearly shown in Figs. 3 and 6, the lower ends of the two die members18 are shaped to force the part of the flange which they engagedinwardly over the upper shoulder 8. Preferably these flange-engagingparts of the dies are notched to provide tooth-like projections A Fig. 3with spaces, as B, between them. Conse uently,'when the upper die isforced towar the lower die, these members will force the parts of theflange which they engage inwardly over the shoulder 8 into the crimpedor turned-in position in which they are shown in Figs. 1 and 4. When theupper die 18 recedes, the plug is turned or indexed into position forthe next downward stroke of the die; and this operation is continueduntil the points of operation of the upper die have been transferredcompletely around the flange and the entire flange has been crimped overthe upper shoulder of the insulator. It sometimes is preferable tooperate twice around the flange in this manner.

It will now be understood that according to this process only asmallpart of the flange is distorted at one time and that by operating on theflange at diametrically opposed points and equalizing the pressureapplied to these points, a very great pressure can be applied to eachpoint of operation so that the firm clamping of the insulator intheshell is insured. At the same time, if the enlargement 7 of theinsulator is higher on one side than the other, which practically alwaysis the case, the flange is turned over against the upper shoulder atboth sides with substantially the same pressure, notwithstanding thesevariations in height. For the sake of economy in manufacture, it ispreferable to perform the crimping operationallows the metal to flowlaterally in opposite Y direction from the points at which the greatestdistortion of the metal of the flange is taking place and thus avoidsthe danger of cracking the flange which otherwise Imght provetroublesome in attempting to crimp it while in a cold condition.

This process produces a flange that varies in thickness and also indensity at successive points circumferentially of the flange and thisconstruction of the flange is of advantage in stiffening it and enablingit better to resist any tendency to spring back or return toward itsoriginal position. This construction, however, is not regarded asabsolutely essential in the finished plug provided the flange is made ofsuflicient thickness and these corrugations may be turned off if desiredafter the plug has been completed. The variation in density of theflange will still be present, however, as will also the variation indensity lengthwise of the flange due to its being turned inwardly.

Preferably the gaskets 10 and 1 1 conslst simply of washers made of somesoft metal, such as copper. This material protects the shoulders of theinsulator from IlIlJIlIY which they might otherwise sustain by contactwith the harder metal of which the shell is made, and at the same timeit does not yield sufficiently to relieve the firm clamping pressurewhich the flange 12 exerts on the upper shoulder 8. It is found inpractice that satisfactory results are obtained by applying to the upperdie a pressure of approximately 2,000 lbs, in performing the crimpingoperation. This pressure is equalized between the two die members 18 sothat substantially 1,000 lbs. are applied to each member at eachoperative stroke of the plunger. It is obvious that the upper die membercould be arranged to operate simultaneously at more than two points onthe flange, if desired, but such an arrangement would require theapplication of considerable morepressure to the die mechanism inorderapply the same amount of pressureto ca point at which the distortion orcrimping of the flange is taking place. Accordingly, I prefer to arrangethe apparatus as shown. But whether the crimping action takes placesimultaneously at two or more points, it is preferable to have thesepoints spaced apart at substantially uniform distances circumferentiallyof the flange, and to equalize the pressure used so that the pressureapplied at jitrouble, this difliculty can be obviated by each point willbe substantially the same as that applied at any other point. Thisarrangement is of material advantage in pre venting the breakage of theinsulators in casethe enlargement of the shoulder is appreciably higheron one side than on the other and also in producing a gas tight jointbetween the insulator and the shell.

In making spark plugs of this general type according to the methodsheretofore practised, the use of a relatively soft gasket between thelower shoulder 9 and the seat 4: has been relied upon to produce a gastight oint because it was found practically impossible to make a gastight joint at the upper end of the enlargement 7 and still use thefir'mer gasket which seemed advantageous at this point. The presentmethod,

however, produces a gas tight joint at the upper end of the enlargement7 notwithstanding substantial variations in the height of thisenlargement at this point circumferential ly thereof. This result isproduced by crlmping only relatively small parts of the flange 12 at atime and equalizing the pressure between the points at which thecrlmping operation is taking place, so that when this operation iscompleted, the flange is shaped to conform the upper gasket to thecontour of the upper shoulder 8 and maintains a substantially uniformpressure on sa1d gasket at all points circumferentially thereofnotwithstanding the variations in the height of said enlargement. Ifdesired the flange 12 may be grooved internally, as indicated at 38,Fig. 7 to provide annular grooves and ribs on its inner surface whichenable this part better to grip the upper gasket 14 during the crimpmgoperation, and to exert a better holding action on the gasketthereafter. This construction however is not usually necessary.

As above stated, a lateral clearance is provided between the bore of theshell and the peripheral surface of the enlargement 7 so that, whilethere may be a contact between these surfaces at one or more points,there is no possibility of the shell exerting sufficient pressure on theinsulator laterally thereof to crush the insulator.

' The construction of the plug herein shown and described is such thatany ordinary and reasonable variations in the dimensions of the parts ofwhich it is made up do not interfere with the production of a satisfac--.'itory.iplug. It will be evident from an in spection. of Figs. 2 and 6that any reasonable varia"on in the depth of the counter-bore ofthejplug, in the thickness of the gaskets 1O andfl l, and in the heightof the enlargementsg7 will not be sufiicient to prevent the flange frombeing crimped into clamping relationship to the insulator as abovedejscribed. If, however, due to unusual conditions these variations seemlikely to cause making the flange 12 long enough to take the reducingaction when the flange has been out down to substantially apredetermined height above the shoulder 8 and above the gasket 14.

It is obvious that practically all the operations in the manufacture ofthe shell and in the mounting of the insulator in the shell can beperformed by automatic machinery and that much of the exactnessheretofore required in the manufacture of these parts is eliminated bythis invention. The cost of manufacture of a plug according to thisconstruction and by this method is materially reduced. Furthermore ithas been found from actual practice that this invention solves thedifficulties heretofore experienced in producing a gas tlght ointbetween the insulators and the shells, even when the insulators are verybadly Warped,

and that an unusually small percentage of the insulators are broken inthe process of assembling the plugs.

\Vhat is claimed as new is:

1. A spark plug comprising a shell hav-.

' ing a bore formed therethrough, an insulator positioned in said boreand having a circumferential enlargement with shoulders at the oppositeends of said enlargement, a seat in said shell supporting one of saidshoulders, and a corrugated flange at the outer end of said shell turnedinwardly over the other shoulder of said insulator and clamping theinsulator in the shell.

2. A spark plug comprising a shell having a bore formed therethrough, aninsulator positioned in said bore and having a circumferentialenlargement with shoulders at the opposite ends of said enlargement, aseat in said shell supporting one of said shoulders, and a flange at theouter end of said shell turned inwardly over the other shoulder of saidinsulator to secure the inextending ribs in its outer face and annularribs in its inner face. 4. A spark plug comprising a shell havtorpositioned in said bore and havin a.-

circumferential enlargement with shoul ers at the opposite ends of saidenlargement, a. seat in said shell supporting one of said shoulders, anda flange at the outer end of said shell turned inwardly over the othershoulder of said insulator to secure the insulator in the shell,successive portions of "said flange both circumferentially andlongitudinally thereof being of different densities.

6. A spark plug comprising a shell having a bore formed therethrough, aninsula- .tor positioned in said bore and having a circumferentialenlargement with shoulders at the opposite ends of said enlargement, aseat in said shell supporting one of said shoulders, and a flange at theouter end of said shell turned inwardly over the other shoulder of saidinsulator to secure the insulator in the shell, said flange varyingsubstantially in thickness at successive points circumferentiallythereof.

7. A spark plug comprising a shell having a bore formed therethrough, aninsulator positioned in said bore and having a circumferentialenlargement with shoulders at the opposite ends of said enlargement, aseat in said shell supporting one of said shoulders, the distancebetween said shoulders varying appreciably at different pointscircumferentlally of said enlargement, and an annular flange at theouter end of said shell turned inwardly over the other shoulder andexerting a substantially uniform pressure on said enlargement at allpoints cireumferentially thereof.

8, A spark plug comprising a shell having a bore formed therethrough, aninsulator positioned in said bore and having a circumferentialenlargement with upper and .lower shoulders, respectively, at the oppo--s1te ends of said enlargement, a seat in said shell supporting thelower of said shoulders, and a flange at the outer end of said shell,integral with the shell, and turned inwardly over the upper shoulder,said enlargement varying appreciably in height at different pointscircumferentially thereof, and said flange being shaped to exert asubstantially uniform pressure on said u per shoulder at all pointscircumferentially thereof and thereby'to clamp said enlarge ment againstsaid seat.

. 9. That improvement in the method of securing an insulator having acircumferential enlargement with upper and lower shoulders,respectively, at the oppositeends of said enlargement, in a spark plugshell having an internal seat for the lower of said shoulders, whichconsists in forming a flange in the outer end of said. shell, placingsaid insulator in the shell, and turning said flange inprogressivelyover the upper shoulder of the insulator into clamping relationshiptherewith.

10. That improvement in the method of securing an insulator having acircumferential enlargement with upper and lower shoulders, respectivelyat the opposite ends of said enlargement, in a spark plug shell havingan internal seat for the lower of said shoulders, which consist informing a flan e in the outer end of said shell, placing said insulatorin the shell, and acting on a relatively small part only of said flangeat a time, and with a substantial predetermined force, to force itinwardly over said upper shoulder into position to clamp said en-' tialenlargement with upper and lower shoulders, respectively, at theopposite ends of said enlargement, in a spark plug shell having aninternal seat for the lower of said shoulders, which consists in forminga flange in the outer end of said shell, placing said insulator in theshell, and turning said flange inwardly over said upper shoulder 1n sucha manner that the flange will exert substantially a uniform pressure onsaid upper shoulder at all points circumferentially thereofnotwithstanding variations in the height of the enlargement.

' 12. That improvement in the method of securing an insulator having acircumferential enlargement with upper and lower shoulders,respectively, at the opposite ends of said enlargement, in a spark plugshell having an internal seat for the lower of said shoulders, whichconsists in forming a flange in the outer end of said shell, placingsaid insulator in the shell, and turning said flange inwardly over saidupper shoulder while the flange is at substantially normal temperaturein such a manner that the flange will exert substantially a uniformpressure on said upper shoulder at all points circumferentially thereofnotwithstanding variationsin the height of the enlargement.

13. That improvement in the method of securing an insulator having acircumferential enlargement with upperand lower shoulders, respectively,at the opposite ends of said enlargement, in a spark plug shell havingan internal seat for the lower of said shoulders, which consists informing a flange above the upper shoulder of the insulator,

and turning said flange inwardly over said upper shoulder in such amanner that the flange will exert substantially a uniform pressure onsaid upper shoulder at all points 'circumi'erentially thereof.notwithstanding variations in the height of the enlargement. I 14. Thatimprovement in the method of securing an insulator havingacircumferential enlargement with upper and lower shoulders,respectively, at the opposite ends of said enlargement, in a spark plugshell having an internal seat for the lower of said shoulders, whichconsists in forming said shell with a relatively thin annular flange atits outer end, inserting said insulator in the shell, and turning saidflange in over the upper shoulder progressively by operating on a smallpart only of the flange at a time and allowing part of the metal of theflange to flow laterally'away from each point of operatlon.

' 15. That improvement in the method of securing an insulator having acircumferentlal enlargement with upper and lower shoulders,respectively, at the opposite ends of said enlargement, in a spark plugshell having an internal seat for the lower of said shoulders, whlchconsists in forming said shell w1th a relatively thin annular flange atits outer end, inserting said insulator in the' shoulder into clampingrelationship therewith 'while the flange is at substantially normaltemperature by operating on said flange at points spaced apart atsubstantially equal distances circumferentially of the flangeandapplying substantially the same'pressure to each of said points, andtransferring said points of operation around the flange until saidcrimping operation is completed. 16. That improvement in the'method ofsecuring an insulator having a circumferential enlargement with upperand lower shoulders, respectively, at the opposite ends of saidenlargement, in a spark plug shell having an internal seat for the lowerof said shoulders, which consists in forming said shell witha relativelythin annular flange at its outer end, inserting said insulator in theshell, and turning said flange over the upper shoulder progressivelyinto clamping relationship therewith by operating on it simultaneouslyat substantially diametrically opposite points and equalizing thepressure applied tosaid points.

17. A spark plug comprising a shell having a bore formed therethrough,an insulator positioned in said bore and having a circum ferentialenlargement with upper and lower shoulders,-respectively, at theopposite ends largement varying appreciably in height atdifl'erentpoints circumferentially thereof, and a gasket on said upper shoulder,said flange being shaped to conform said gasket to said upper shoulderand to maintain a substantially uniform pressure on said 10 gasket atall points circumferentially thereof notwithstanding said variationsinthe height of said enlargement.

In testimony whereof I have signed my name to this specification.

FREDERICK M. F URBER.

